The present invention relates to a control device for an at least part-time four-wheel-driven motor vehicle. More particularly, the present invention relates to a control device for an at least part-time four-wheel-driven motor vehicle, having a control unit which variably distributes driving torque of a drive unit to primary driving wheels, which are permanently connected with the drive unit, and to secondary driving wheels which, if required, can be connected by way of a transfer clutch with the drive unit, wherein the control unit determines a desired clutch torque which is to be set by an actuator device at the transfer clutch.
A control device of this type is described, for example, in German Patent Document DE 100 54 023 A1. Accordingly, a torque distribution device is known for changing the torque distribution ratio between the wheels of the front axle and the wheels of the rear axle by a corresponding control of a friction clutch as a longitudinal blocking device (i.e., transfer clutch).
In general, as described below, primary driving wheels are the wheels which are permanently connected with the drive unit, and secondary driving wheels are the wheels which, if required, can be connected with the drive unit by way of the transfer clutch.
In the case of the known control devices, only one control unit is known for controlling or regulating the torque distribution or the clutch torque at the transfer clutch, which control unit computes the desired clutch torque and converts the computed desired clutch torque to an electric control signal for the actuator device of the transfer clutch.
It is an object of the present invention to improve a control system of the previously mentioned type with a view to improving the precision of the control, while the expenditures and costs are simultaneously reduced.
The present invention is based on the recognition that a physical division of the control unit into a master-like main control unit and into an additional control unit in the form of an intelligent final stage has the following advantages.
By using input signals and physical models, which normally are present in certain motor vehicle systems for other driving-dynamics-related control functions, as parameters in the main control unit, an unrestrictedly precise driving-dynamics-related driving performance can be provided. This can be achieved without additional expenditures if the main control unit is integrated in a control device, which has already been provided for other driving-dynamics-related systems. The electronic control device for the brake controlling functions (known, for example, by the abbreviations ABS/ASC, DSC, FDR) is particularly advantageous for this purpose.
Furthermore, an improvement of emergency running characteristics may be achieved as a result of possible redundancies.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.